Process of producing c3h4 aliphatic hydrocarbons and ethylene from propylene



PROCESS OF PRODUCING C l-I ALIPHATIC HYDROCARBONS AND ETHYLENE FROMPROPYLENE Willis C. Keith, Lansing, Robert H. Elkins, Flossmoor, andRobert R. Chambers, Park Forest, llll., assignors to Sinclair RefiningCompany, New York, N.Y., a corporation of Maine Filed June 21, 1954,Ser. No. 438,300

9 Claims. (Cl. 260-678) No Drawing.

. version of propylene.

Although the production of acetylene has been established on acommercial basis for many years, there has not to our knowledge beenproposed any low cost method for producing C H aliphatic hydrocarbons ingood yields at commercially acceptable conversion levels. The C Haliphatic hydrocarbons include methyl acetylene, the first homolog ofthe acetylene, and allene, the isomer of methyl acetylene. Either ofthese hydrocarbons is readily converted to the equilibrium mixture whichheavily favors methyl acetylene at ordinary temperatures. Hightemperature methods of preparation lead to mixtures of thesehydrocarbons; however, this result is not a serious drawback since bothcompounds will give the same chemical derivatives in many reactions andif necessary they can be separated by either physical or chemical means.The C H hydrocarbons are useful in preparing many chemical compounds.For instance, the addition of alcohols to methyl acetylene or allenetakes place in the presence of bases to form isopropenyl ethers whichpolymerize readily in the presence of acidic catalysts. Among the othermaterials which may be added the products from the cracking of lowmolecular weight hydrocarbons, they have until recently beenunsuccessful.

Szwarc in J. Chem. Phys., 17, p. 284 (1949) pyrolyzed 5 propylene at areduced pressure and a temperature of to the C H hydrocarbons arecarboxylic acid, hydrochloric acid, chlorine, mercaptans, andhydrocyanic acid. There have been a number of methods proposed formanufacturing methyl acetylene. Among these are included thedehydrohalogenation of propylene dibromide, the reaction of sodiumacetylide with methyl iodie in liquid ammonia, the pyrolysis ofquaternary ammonium salts, the electrolysis of sodium crotonate and thepyrolysis of diketene. These methods are more or less representative oflaboratory scale preparations. One process which has been consideredfrom a commercial standpoint includes the production of methyl acetyleneby hydrolysis of Mg C During World War II the Germans made aconsiderable study of this method and issuance of US. Patent 2,510,550may indicate recent interest in this process in this country. However,to our knowledge this latter method is not in commercial practice.

We believe the most promising commercial method of producing C Haliphatic hydrocarbons is through the utilization of a vapor phasecracking or dehydrogenation process. Apparently the occurrence of methylacetylene in cracked products is not uncommon although it is usuallyfound only in very small percentages. This product was isolatedcommercially as a by-product in the electric arc process for makingacetylene from methane, and .there are also several patents directed tothe removal of methyl acetylene formed in making butadiene. Of coursethe process of most potential interest is one in which methyl acetyleneis obtained in good yields by converting an inexpensive raw material.Although workers have for some time searched for methyl acetylene inabout 680 to 870 C. His experiments were run at very low conversions(0.01 to 2 weight percent of the feed).

Rice in U.S. Patent 2,429,566, has indicated that most earlier workershad obtained tars and liquid products when they cracked isobutyleneunder conditions which he felt should give methyl acetylene. Thepatentee pyrolyzed isobutylene in a quartz tube and indicated thatreaction conditions might include temperatures of 700 to 900 C. andpressures of about to A atmospheres while employing about 0.5 to 5.0seconds contact time. Rice regulated these conditions so that beoperated just short of the point at which tar and liquid products formedand be indicated that propylene could be employed as the starting olefinalthough he apparently did not effect this reaction.

In the present invention we have devised a process for manufacturing C Haliphatic hydrocarbons and ethylene at commercially feasible yieldlevels. The value and uses of ethylene are well-known and do not needelaboration. In our process we subject propylene to a temperatureranging from about 1300 F. to the decomposition temperature of the C Hhydrocarbon product under the reaction conditions and the olefin partialpressure is not greater than about one atmosphere. Further our reactionis conducted in the presence of at least an equal molar quantity (basedon the propylene) of a gas inert and not deleterious to the desiredreaction. In this process to produce more advantageous yields of thedesired products, the conversion of the propylene should not be greaterthan about 80 weight percent of that charged to the reaction zone.

The feed to our process is propylene; however, it can be a mixture ofpropane and propylene containing up to about by volume of propane. Whenusing mixtures of propane and propylene we prefer that they not con tainmore than about 10% by volume of propane in order to produce moreadvantageous yields of the C H hydrocarbons. In operation of our processthe feed can be converted either on a once-through or a recycle basis.

The temperature of our reaction can vary from about 1300 F. to thedecomposition temperature of the 0 H, hydrocarbon product under thereaction conditions. However, we prefer reaction temperatures of about1400 to 1800 F. These temperatures can be produced by passing thepropylene-inert gas mixture through an externally heated reaction tubeto raise them simultaneously to reaction temperature. However, weparticularly prefer that the inert gas be preheated to a temperaturesufliciently above the reaction temperature to heat the feed to reactiontemperature. Propylene feed is supplied to the reaction zone as a vaporat a temperature sulficiently below reaction temperature that the feedis substantially unreacted until mixing with the inert gas, andaccordingly the exact temperature of the preheated inert gas will dependupon the temperature of the incoming feed, the ratio of the propylene tothe inert gas, as well as the desired reaction temperature to bemaintained while taking into account the heat supplied to the reactionzone .by indirect heat exchange. As an example, the temperature of theinert gas may be in the range of about 1500 to 2000 F.; however, atemperature should not be used which is high enough to destroy its inertstate. The present process is most advantageously conducted at atmospheric pressure although elevated pressures such as 2 or 3atmospheres or subatmospheric pressures may be employed. However, thepartial pressure of the propylene feed should not exceed about oneatmosphere.

Among the non-reacting gases which can be employed as the inert gas inour process is steam which is preferred; however, other inert gases ortheir mixtures can be utilized such as nitrogen, carbon dioxide andmethane. As previously noted, the amount of inert gas passed to thereaction zone is at least 1 mole per mole of propylene feed. Althoughthere is no theoretical upper limit on the amount of inert gas which canbe employed, it would hardly be economically feasible to use more thanabout 40 moles of inert gas per mole of propylene. A preferred ratio ofinert gas to propylene feed is about to 40 moles per mole. Increasingthe amount of inert gas results generally in increased yields of QR;hydrocarbons. The increase of the inert gas also results in decreasedcoke formation; however, from the commercial point of view the exactinert gas ratio employed will be determinedby compromise between thebeneficial results obtained and the heating costs incurred.

We have found that the yields of C l-I hydrocarbons and ethylene in ourprocess are essentially functions only of the percent of the feedconverted. Therefore, temperature and contact time are equivalentvariables for controlling the degree of conversion at a given propylenepartial pressure and inert gas to propylene ratio. At very lowconversions the yield of C H hydrocarbons approaches about 35 weightpercent of the propylene converted, and as the conversion increases sayto 100% the C l-L; yield apparently decreases to the neighborhood ofabout weight percent of the propylene converted. Ethylene yield at verylow conversions is just above weight percent of the propylene converted.Ethylene yield is at a maximum of about 40 weight percent between aboutto 55 weight percent conversion of the propylene, and the yield thenapparently decreases to just below 25 at 100% conversion. Acetylene andC production varies from 15 to 5 weight percent over the conversionrange. Thus to obtain more desirable yields of the C H hydrocarbon andethylene, we have found that the reaction conditions includingtemperature, contact time, and ratio of inert gas to propylene should belimited in severity so that not more than about 80% by weight, based onthe propylene charged to the reaction zone of the feed is converted. Theyield can be as low as desired and still produce a substantial amount ofthe C H hydrocarbon and ethylene. However, we prefer to maintain theconversion of the propylene from about 20 to 80 weight percent basedupon the propylene charged to the reaction zone. Our work has indicatedthat allene may be the principal immediate C H product of our reactionand that methyl acetylene may be formed by isomerization.

Although our reaction may be conducted with simultaneous heating of thesteam and propylene vapors to reaction temperature, we particularlyprefer to employ the method in which the inert gas is preheated to 'atemperature above the reaction temperature to raise the propylene to thetemperature of reaction through mixing in a reaction zone with the feed.Thus the temperature of the propylene feed should be below that which areaction would be effected before being mixed with the preheated inertgas to bring the propylene to reaction temperature. The simultaneousheating of the inert gas and propylene leads to excessive reactor walltemperatures which give rise to considerable coking. Further difficultyis experienced in the latter reaction in achieving constant temperaturedistribution in the reactor.

Our most successful reactor comprised an upper furnace section about 3feet long surrounding a mm. quartz reactor tube which extendeddownwardly through a second furnacesection about 1 foot long. The twofurnace sections were separated by glass wool insulation. A water inletwas provided in the quartz tube at its upper end just above the firstfurnace section. Extending downwardly through the first furnace sectionand into the second furnace section was a platinum/platinum-rhodiumthermocouple for indicating the temperature of the reaction. Between thetwo furnace sections and at the glass wool insulation was provided apropylene inlet tube leading into the quartz reactor. The lower end ofthe reactor tube opened into a coil condenser which was cooled by waterand provided recovery of gases and condensed liquids. The section of thequartz tube surrounded by the first furnace section preheated the inertgas to a temperature above the reaction temperature. The inert gas thenflowed downwardly into the reactor section of the quartz tube packedwith ceramic beads and surrounded by the second furnace section, and thegas was mixed with the propylene feed as it passed the hydrocarboninlet. The furnace surrounding the reactor section of the tube wasmaintained at the reaction temperature to prevent heat loss. The resultsobtained with the use of this reactor system were considerably betterthan those produced in reactors providing for heating the inert gas andpropylene feed to reaction temperature after their mixture by passagethrough a hot reaction tube.

It has been found desirable to conduct our reaction in a quartz reactor.For instance, the yields of C H hydrocarbons in a stainless steelreactor are considerably lower than those obtained in a quartz reactor.There is an indication that although the primary reactions follow thesame course in both of these reactors, the stainless steel catalyzes theconversion of the C H hydrocarbons to carbon monoxide, carbon dioxideand hydrogen in the presence of steam.

The separation of the C H aliphatic hydrocarbons andethylene from ourreaction mixtures can be effected either by chemical or physical meansbut the latter method is more desirable. For instance, anethylene-containing fraction and the C H aliphatic hydrocarbons can beseparated from their reaction mixture by fractionation. Ethylene can beseparated from its fraction by conventional procedures.

In order to illustrate our invention in more detail we include thefollowing specific examples which are not to be considered limiting. Thereaction of each of the examples was conducted in the reactor describedabove in detail.

EXAMPLE I Water was pumped to the top section of the reactor by aproportioning pump and passed downwardly through the quartz reactoropposite the top furnace section maintained at a temperature sufiicientto vaporize and preheat the resulting steam to 1800 F. by the time itreached the propylene feed inlet tube. Propylene (5% propane) wasvaporized and passed through the feed inlet tube and mixed with thepreheated steam. The mole ratio of steam to propylene feed in themixture was 40 to l. The flow rates of the feed and inert gas wereregulated so that their contact time at reaction temperature was 0.080second. The reaction temperature maintained was a mean 1570 F. Thebottom furnace section was employed to control the temperature in thereaction zone and prevent heat losses. The reactor section was broughtto reaction temperature by passage of steam and control of the furnacetemperatures before propylene was admitted to the reactor. The reactionproducts were passed to a water coil condenser and the steam andcondensable gases were collectedin traps cooled by Dry Ice and acetone.The non-condensable gas was measuredby a wet test meter and a composite.gas sample was taken for mass spectrometer analysis. The materialscondensed were submitted for low temperature distillation andthe C C and0 fractions were analyzed on amass spectrometer. The amount of cokeformed was determined from analysis of the non-condensable gas (CO andCO inert gas were calculated from the free space of the reactor and thevolume of gases at reaction temperature.

The run just described was No. 540-63 and the total conversion was 22.5weight percent based on the propylene feed charged to the reactor. Theproduct analysis based upon the weight percent of the feed charged isexpressed in Table I which also shows the results obtained in severalother runs in Examples II toIV made with the same propylene feed underconditions essentially as described in run No. 544-63 but with thechanges noted in the table. Similar conditions were observed in ExamplesV and VI but the feed was 99% pure propylene in Example V and 50%propylene-50% propane in Example VI.

Table 1 1321.1 EX.II Ex.III Ex.IV Ex.V Ex.VI

Run Run Run Run Run Run 540-63 540-72 540-64 540-67 540-81 540-69Reaction Temp,

F. (mean) 1,570 1,520 1,675 1,670 1,575 1,480 Contact time,

seconds 0.080 0.065 0.0765 0.146 0.129 0.068 Steam/propylene,

mole ratio 40 40 40 40 40 40 Total conversion,

Wt. percent 22.5 5.7 45.2 62.1 21.1 10.4 Products, Wt. percent ofpropylene feed:

a 9. 4 1. 6 16. 3 22. 2 7. 9 3. 3 01H; 5.2 1.7 8.1 8.8 4.8 1.2 Ultimateyield, Wt.

percentz' 1 Based on propane decomposed. 9 Based on 100% materialbalance.

We claim:

1. The method of producing C H aliphatic hydrocarbons and ethylene whichcomprises subjecting propylene to a temperature from about 1300 F. tothe decomposition temperature of the C H product under the reactionconditions, at a partial pressure of propylene not greater than aboutone atmosphere in the pressure of at least an equal molar quantity of aninert gas and recovering C l-I aliphatic hydrocarbons and ethylene fromthe reaction products.

2. The, method of claim 1 in which the inert gas is steam.

3. The method of claim 1 inwhich the reaction is carried out in a quartzreaction zone.

4. The method of claim 1 in which the conversion of the propylene is notmore than about weight percent.

5. The method of producing (1 H, aliphatic hydrocarbons and ethylenewhich comprises subjecting in a quartz reaction zone propylene to atemperature from about 1300 F. to the decomposition temperature of the 01-1 product under the reaction conditions at a partial pressure ofpropylene not greater than about one atmosphere in the presence of atleast an equal molar quantity of steam which is preheated above thereaction temperature and then mixed with the propylene to bring it toreaction temperature while limiting the conversion of the propylene tonot more than about 80 weight percent and recovering C H aliphatichydrocarbons and ethylene from the reaction products.

6. The method of claim 5 in which the conversion of the propylene islimited to about 20 to 80 weight percent.

7. The method of claim 6 in which the steam is present in the ratio ofabout 5 to 40 moles per mole of the propylene.

8. The method of producing C H aliphatic hydrocarbons and ethylene whichcomprises subjecting propylene to a temperature from about 1300 F. tothe decomposition temperature of the QR; product under the reactionconditions at a partial pressure of propylene not greater than about oneatmosphere in the presence of at least an equal molar quantity of aninert gas which was preheated above the reaction temperature and thenmixed with the propylene to bring it to reaction temperature andrecovering C H aliphatic hydrocarbons and ethylene from the reactionproducts.

9. The method of claim 8 in which the inert gas is steam.

References Cited in the file of this patent UNITED STATES PATENTS1,986,876 Baxter et al. Jan. 8, 1935 2,429,566 Rice Oct. 21, 19472,649,485 Taylor et a1 Aug. 18, 1953 2,719,872 Happel et al. Oct. 4,1955 2,752,405 Happel et al. June 26, 1956

1. THE METHOD OF PRODUCING C3H4 ALIPHATIC HYDROCARBONS AND ETHYLENEWHICH COMPRISES SUBJECTING PROPYLENE TO A TEMPERATURE FROM ABOUT 1300*F.TO THE DECOMPOSITION TEMPERATURE OF THE C3H4 PRODUCT UNDER THE REACTIONCONDITIONS, AT A PARTIAL PRESSURE OF PROPYLENE NOT GREATER THAN ABOUTONE ATMOSPHERE IN THE PRESSURE OF AT LEAST AN EQUAL MOLAR QUANTITY OF ANINERT GAS AND RECOVERING C3H4 ALIPHATIC HYDROCARBONS AND ETHYLENE FROMTHE REACTION PRODUCTS.